Inclined rotation control device of variable displacement hydraulic pump

ABSTRACT

A motion converting section ( 31 ) and a translation bar ( 33 ) of a feedback mechanism ( 30 ) are provided between a lateral side of a swash plate ( 21 ) and a control sleeve ( 26 ) of a regulator ( 24 ). When the swash plate ( 21 ) is in a neutral position, the motion converting section ( 31 ) is located in an initial position (F-F) at one end of axial direction along an axis line (O-O) passing through a tilting center (C) of tilting motions, and, when the swash plate ( 21 ) is driven to tilt in a forward or reverse direction, displaced to the other end of axial direction along the axis line (O-O) to convert a tilting motion of the swash plate ( 21 ) into an axial displacement. Through the translation bar ( 33 ), the axial displacement is transmitted to the control sleeve ( 26 ) of the regulator ( 24 ) as an axial displacement.

TECHNICAL FIELD

This invention relates to a tilting controller for a variabledisplacement hydraulic pump suitable for use, for example, on a workingvehicle such as wheel loader, wheel type hydraulic excavator orhydraulic crane or crawler type hydraulic excavator or hydraulic powercrane.

BACKGROUND ART

Generally, construction machines like hydraulic excavators are providedwith a variable displacement hydraulic pump which constitutes a pressureoil source along with a tank. A rotational shaft of a variabledisplacement hydraulic pump of this sort is driven from a prime moverlike a Diesel engine to supply pressure oil to and from varioushydraulic actuators such as working hydraulic cylinders, a vehicle drivehydraulic motor or a revolving hydraulic motor.

There has conventionally been known a variable displacement hydraulicpump of this sort (hereinafter referred to as a first prior art) whichis provided with a tilting controller, including tilting actuators towhich a tilting control pressure is supplied to drive tilting motions ofa volume varying portion of the hydraulic pump, a regulator in the formof a servo valve having a spool within a control sleeve for controllingthe tilting control pressure to be supplied to and from the tiltingactuators according to a command signal from outside, and a feedbackmechanism which is adapted to follow tilting motions of the volumevarying portion for feedback control of the control sleeve of theregulator (e.g., Japanese Patent Laid-Open No. 2003-74461).

In the case of the tilting controller just mentioned, as the spool ofthe regulator is put in a sliding displacement in response to a commandsignal from outside, the tilting control pressure is switched to let thetilting actuators drive the volume varying portion. The feedbackmechanism is arranged, for example, to turn a feedback link, followingtilting motions of the volume varying portion. Further, by transmissionof a rotational displacement of the feedback link, the control sleeve ofthe regulator is put in a sliding displacement in the same direction asthe spool for the sake of feedback control.

On the other hand, as a second prior art, there has also been known atilting controller for a variable displacement hydraulic pump, which isarranged for application exclusively to a closed hydraulic circuit(e.g., Japanese Patent Laid-Open No. H5-39863).

In the case of the tilting controller employed in the variabledisplacement hydraulic pump by the above-mentioned first prior art, avolume varying portion of the hydraulic pump is driven to tilt only inone direction (e.g., in a normal or forward direction), for example, inreference to a zero angle neutral position, without taking into accounttilting motions in a reverse direction from the neutral position.

Therefore, in order to connect the variable displacement hydraulic pumpto a hydraulic actuator like a hydraulic motor through a closedhydraulic circuit, drastic restructuring becomes necessary for drivingthe volume varying portion to tilt in both forward and reversedirections from the neutral position.

Besides, when applied to a closed hydraulic circuit, the control sleeveof the regulator has to be fed back (put in sliding displacements) inboth forward and reverse directions as the volume varying portion istilted in forward and reverse directions, and this makes smooth feedbackcontrol of the regulator difficult.

On the other hand, in the case of the tilting controller of the variabledisplacement hydraulic pump by the second prior art which is intendedspecifically for use with a closed hydraulic circuit, a tilting actuatorwhich drives a volume varying portion of the hydraulic pump is assembledintegrally with a volume control valve.

More particularly, in this case of the tilting controller, main spoolsand pressure chambers are provided on the opposite sides of a regulatorpiston which functions as a tilting actuator, necessitating an increasednumber of component parts due to complicate construction of thecontroller as a whole.

Besides, in this case, the tilting controller which is constructedexclusively for use with a closed hydraulic circuit is too limited inversatility to exclude applications to an open hydraulic circuit, thatis to say, can find only limited applications as a hydraulic pump.

DISCLOSURE OF THE INVENTION

In view of the above-discussed problems with the prior art, it is anobject of the present invention to provide a tilting controller for avolume varying portion, which can drive a volume varying portion to tiltin both forward and reverse directions to permit application to a closedhydraulic circuit and which is capable of smooth feedback control of aregulator, despite simplification in construction.

It is another object of the present invention to provide a tiltingcontroller for a variable displacement hydraulic pump, which not onlycan be connected to a hydraulic actuator of a hydraulic motor by the useof a closed hydraulic circuit but can be applied to an open hydrauliccircuit, succeeding in attaining higher versatility of application andhigher productivity while cutting a production cost.

(1) According to the present invention, in order to achieve theabove-stated objectives, there is provided a tilting controller for avariable displacement hydraulic pump, including a variable displacementhydraulic pump having a volume varying portion in association with arotational shaft rotationally driven by a drive source, tiltingactuators adapted to be applied with a tilting control pressure fordriving the volume varying portion of the hydraulic pump into a tiltedposition, a regulator in the form of a servo valve having a spool withina control sleeve for generating the tilting control pressure to be fedto and from the tilting actuators according to a command signal fromoutside, and a feedback mechanism adapted to follow tilting motions ofthe volume varying portion to feed back the control sleeve of theregulator.

The tilting controller according to the invention is characterized inthat the volume varying portion of the hydraulic pump is tiltable inboth forward and reverse directions from a zero angle neutral positiondriven by the tilting actuators; the feedback mechanism is constitutedby a motion converting section adapted to convert a tilting motion ofthe volume varying portion into a longitudinal linear displacement alonga straight line passing a tilting center of the volume varying portion,and a displacement transmission member located between the motionconverting section and the control sleeve of the regulator to transmitthe longitudinal linear displacement converted by the motion convertingsection to the control sleeve of the regulator; and the motionconverting section being located in an initial position at one end oflongitudinal direction along the straight line when the volume varyingportion is in a neutral position, and being displaced along and towardthe other end of longitudinal direction along the straight line from theinitial position when the volume varying portion is driven to tilt inforward or reverse direction.

As described above, according to the present invention, by means oftilting actuators, a volume varying portion of a hydraulic pump in aneutral position can be driven to tilt in both forward and reversedirections. Therefore, when the volume varying portion is tilted in aforward direction, for example, pressure oil can be supplied from thehydraulic pump to a hydraulic actuator in one direction through a closedhydraulic circuit. On the other hand, when the volume varying portion istilted in a reverse direction, pressure oil can be supplied from thehydraulic pump to a hydraulic actuator in the opposite direction(reverse direction). Besides, the feedback mechanism is constituted by amotion converting section and a displacement transmission member, and,when the volume varying portion is in a zero angle neutral position, themotion converting section of the feedback mechanism is located at aninitial position at one end of longitudinal direction along a straightline passing through a tilting center of the volume varying portion.When the volume varying portion is driven into a tilted position inforward or reverse direction, a tilting motion of the volume varyingportion is converted into a longitudinal linear displacement along theabove-mentioned straight line, that is to say, into a longitudinallinear displacement toward the other end of longitudinal direction fromthe initial position. The linear displacement is transmitted from thedisplacement transmission member to the control sleeve of the regulator,putting the control sleeve in a sliding displacement in the samedirection of a spool to feed back the regulator.

Therefore, even in a case where the hydraulic pump is connected to ahydraulic actuator through a closed hydraulic circuit, the volumevarying portion can be tilted in both forward and reverse directions tocontrol the delivery rate (flow rate) of pressure oil in bothdirections, under smooth feedback control of the regulator no matterwhether the volume varying portion is tilted in forward or reversedirection. Since the regulator can be constituted by a servo valvehaving a spool within a control sleeve, the tilting controller as awhole can be simplified in construction. Further, the hydraulic pump canalso be applied to an open hydraulic circuit for supplying pressure oilto and from a hydraulic actuator. Namely, the hydraulic pump is of aversatile build which can be applied to both closed hydraulic circuitsand open hydraulic circuits, and which can contribute to enhanceproductivity and to cut production cost.

(2) In this instance, the above-mentioned straight line extends parallelwith an axis line of the rotational shaft of the hydraulic pump, and themotion converting section is adapted to convert a tilting motion of thevolume varying portion into an axial displacement along the direction ofthe axis line of the rotational shaft.

With the arrangements just described, by the motion converting sectionof the feedback control mechanism, a tilting motion of the volumevarying portion can be converted into an axial displacement along thedirection of the axis line of the rotational shaft of the hydraulicpump. When the volume varying portion is in the neutral position, forexample, the displacement transmission member of the feedback mechanismis located in the initial position at one end of axial direction longthe direction of the rotational shaft of the hydraulic pump, and, whenthe volume varying portion is driven to tilt in forward or reversedirection, the displacement transmission member can be displaced axiallyfrom the initial position toward the other end of axial direction.

(3) Further, in another preferred form of the present invention, theabove-mentioned straight line is an inclined straight-line drawn at apredetermined angle relative to the rotational shaft of the hydraulicpump, and the motion converting section is adapted to convert a tiltingmotion of the volume varying portion into a longitudinal lineardisplacement in the direction of the inclined straight line.

With the arrangements just described, by the motion converting sectionof the feedback mechanism, a tilting motion of the volume varyingportion is converted into a longitudinal linear displacement along theinclined straight line. When the volume varying portion is in a neutralposition, for example, the displacement transmission member of thefeedback mechanism is located in an initial position at one end of alongitudinal direction along the inclined straight line, and, when thevolume varying portion is driven to tilt in forward or reversedirection, the displacement transmission member is displaced from theinitial position toward the other end of the longitudinal direction.

(4) On the other hand, according to the present invention, a directionalcontrol valve is provided between the tilting actuators and theregulator to switch direction of supply of the tilting control pressurefor driving to tilt the volume varying portion in forward or reversedirection from a neutral position.

With the arrangements just described, the direction of tilting controlpressure supply can be changed over from direction to another byswitching the position of the directional control valve which isprovided between the tilting actuators and the regulator, and the volumevarying portion can be tilted in both forward and reverse direction fromthe neutral position according to a tilting control pressure. Besides,the construction of the tilting controller including the regulator canbe simplified from the standpoint of enhancing productivity and cuttingthe production cost.

(5) Further, according to the present invention, the displacementtransmission member of the feedback mechanism is constituted by atranslation member adapted to be put in a rectilinear movement in thelongitudinal direction of the straight line together with the controlsleeve of the regulator, following a tilting motion of the volumevarying portion.

With the arrangements just described, in consequence of a tilting motionof the volume varying portion an axial displacement translated by themotion converting section is transmitted to the control sleeve of theregulator as a rectilinear movement of a translation member in thelongitudinal direction of the straight line, permitting smooth feedbackcontrol of the control sleeve.

(6) Further, according to the present invention, the motion convertingsection of the feedback mechanism is constituted by an active couplingmember provided at a lateral side of the volume varying portion at aposition spaced from a tilting center of the volume varying portion, anda passive coupling member provided at one longitudinal end of thedisplacement transmission member extended in a perpendicularlyintersecting direction relative to the straight line and held in slidingengagement with the active coupling member.

In a case where the motion converting section of the feedback mechanismis constituted by an active coupling member which is provided at alateral side of the volume varying portion, and a passive couplingmember which is provided at one longitudinal end of a displacementtransmission member, a tilting motion of the volume varying portion canbe converted into a rectilinear movement (a longitudinal lineardisplacement) of the displacement transmission member.

(7) Further, in this case, the active coupling member of the motionconverting section is constituted by a projection provided on the volumevarying portion to extend in a radial direction relative to the straightline, and the passive coupling member is constituted by a slider portionof U-shape in cross section slidably held in fitting engagement with theprojection and extended in a perpendicularly intersecting directionrelative to the straight line.

In this manner, by holding the projection slidably in fitting engagementwith the slider portion of U-shape in cross section, one end of thedisplacement transmission member can be restricted of movements relativeto the volume varying portion in the longitudinal direction of theabove-mentioned straight line, but relative movements of the sliderportion and the volume varying portion are permitted in a directionperpendicular to the straight line to pick up smoothly tilting motionsof the volume varying portion.

(8) Further, according to the present invention, the motion convertingsection of the feedback mechanism is constituted by a tilting leverextended from the volume varying portion in the longitudinal directionof the straight line for tilting integrally with the volume varyingportion, an active coupling member provided on the tilting lever at aposition spaced from a tilting center of the volume varying portion, anda passive coupling member provided at one longitudinal end of thedisplacement transmission member to extend in a perpendicularlyintersecting direction relative to the straight line and held in slidingengagement with the active coupling member.

With the arrangements just described, a tilting motion of the volumevarying portion can be converted into a longitudinal linear displacementof the displacement transmission member on a magnified scale dependingupon the length of a hand of the tilting lever, making it possible totransmit a tilting motion of the volume varying portion to the controlsleeve of the regulator on a magnified scale.

(9) In this instance, preferably the active coupling member of themotion converting section is constituted by a projection provided on thetilting lever in a radial direction relative to the straight line, andthe passive coupling member is constituted by a slider portion ofU-shape in cross section slidably held in fitting engagement with theprojection and extended in a perpendicularly intersecting directionrelative to the straight line.

(10) On the other hand, according to the present invention, thedisplacement transmission member of the feedback mechanism isconstituted by a support shaft extended in a direction perpendicular tothe straight line, and a rocking link having a longitudinallyintermediate portion thereof rockably supported on the support shaft todisplace the control sleeve of the regulator in a longitudinal directionfollowing a tilting motion of the volume varying portion.

In a case where a rocking link is employed in this manner, a tiltingmotion of the volume varying portion is converted into a longitudinaldisplacement in the opposite direction by the motion converting section,and it can be transmitted to the control sleeve of the regulator as adisplacement in the opposite direction. Nevertheless, even in this case,the control sleeve is displaced in the same direction as the spool bythe feedback control of the regulator. Further, in this case, as the oneend and the other end of the rocking lever are turned about the supportshaft, they are displaced in opposite directions. Therefore, thedimension of a displacement of the control sleeve can be magnifieddepending upon the ratio of a dimension (the ratio of a length) from thesupport shaft to the both ends of the rocking lever. Accordingly,displacements can be fed back to the control sleeve of the regulator ona sufficiently enlarged scale.

(11) Further, according to the present invention, the motion convertingsection of the feedback mechanism is constituted by an active couplingmember provided at a lateral side of the volume varying portion at aposition spaced from a tilting center of the volume varying portion, anda passive coupling member provided at one longitudinal end of therocking link extended in a perpendicularly intersecting directionrelative to the straight line and held in slidable engagement with theactive coupling member. In this case, a tilting motion of the volumevarying portion is picked up as a rocking displacement of the rockinglink (a rocking displacement in the longitudinal direction of theabove-mentioned straight line).

(12) Even in the foregoing case, the active coupling member of themotion converting section is constituted by a projection provided on thevolume varying portion in a radial direction relative to the straightline, and the passive coupling member is constituted by a slider portionof U-shape in cross section slidably held in fitting engagement with theprojection and extending in a perpendicularly intersecting directionrelative to the straight line.

(13) On the other hand, according to the present invention, the controlsleeve and spool of the regulator are disposed to extend parallel withthe straight line, and the displacement transmission member is fixedlyanchored to the control sleeve.

In this case, for example, the translation member which is providedbetween the control sleeve of the regulator and the volume varyingportion (or the tilting lever) can be smoothly displaced in thelongitudinal direction of the above-mentioned straight line, following atilting motion of the volume varying portion to realize smooth feedbackcontrol of the control sleeve of the regulator.

(14) Further, according to the present invention, the hydraulic pump iscomprised of a tubular casing rotatably supporting the rotational shaft,a cylinder block provided in the casing for rotation integrally with therotational shaft and containing a plural number of cylinders whichextend in axial direction at spaced positions in circumferentialdirection, a plural number of pistons fitted in the cylinders of thecylinder block for reciprocating movements therein, and a swash platehaving a sliding surface for a shoe attached to an end of each pistonand tiltably mounted in the casing to constitute the volume varyingportion; the tilting actuators are located in the casing at a spacedposition from the rotational shaft in radially direction and havingtilting pistons for driving the swash plate in a neutral position totilt in a forward or reverse direction; the regulator is provided in thecasing at a spaced position from the tilting pistons, with the controlsleeve coupled with the swash plate through the feedback mechanism; andan intermediate portion of the displacement transmission member of thefeedback mechanism is mounted on the casing in such a way as to permitdisplacements along the longitudinal direction of the straight line.

With the arrangements just described, even in a case where the swashplate type variable displacement hydraulic pump is connected to ahydraulic actuator through a closed hydraulic circuit, the swash platecan be tilted in forward and reverse directions from a zero angleneutral position, permitting to control the delivery rate (flow rate) ofpressure oil in both directions and feeding back the regulator smoothlyno matter whether a tilting motion of the swash plate is in a forwarddirection or in a reverse direction.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a circuit diagram of a closed hydraulic circuit incorporatinga variable displacement hydraulic pump according to a first embodimentof the present invention;

FIG. 2 is a vertical sectional view of the hydraulic pump shown in FIG.1;

FIG. 3 is a vertical sectional view of the hydraulic pump, taken in thedirection of arrows III-III in FIG. 2;

FIG. 4 is an enlarged sectional view taken in the direction of arrowsIV-IV of FIG. 3, showing a swash plate in a neutral position;

FIG. 5 is a sectional view taken from the same position as FIG. 4,showing the swash plate which has been tilted in a forward direction;

FIG. 6 is a circuit diagram of a tilting controller for the swash platein the first embodiment;

FIG. 7 is a front view showing the swash plate and feedback mechanism ofFIG. 6 along with the tilting pistons;

FIG. 8 is a front view showing the swash plate of FIG. 7 which has beentilted in a forward direction;

FIG. 9 is a front view showing the swash plate of FIG. 7 which has beentilted in a reverse direction;

FIG. 10 is a vertical sectional view taken in the same position as FIG.3, showing a hydraulic pump according to a second embodiment of theinvention;

FIG. 11 is an enlarged sectional view taken in the direction of arrowsXI-XI of FIG. 10, showing a swash plate in a neutral position;

FIG. 12 is a sectional view taken in the same position as FIG. 11,showing the swash plate which has been tilted in a forward direction;

FIG. 13 is a circuit diagram of a tilting controller for the swash platein the second embodiment;

FIG. 14 is a front view showing the swash plate and feedback mechanismof FIG. 13 along with the tilting pistons;

FIG. 15 is a front view showing the swash plate of FIG. 14 which hasbeen tilted in a forward direction;

FIG. 16 is a front view showing the swash plate of FIG. 14 which hasbeen tilted in a reverse direction;

FIG. 17 is a vertical sectional view taken in the same position as FIG.3, showing a hydraulic pump according to a third embodiment of theinvention;

FIG. 18 is an enlarged sectional view taken in the direction of arrowsXVIII-XVIII of FIG. 17, showing a swash plate in a neutral position;

FIG. 19 is a sectional view taken in the same position as FIG. 18,showing the swash plate which has been tilted in a forward direction;

FIG. 20 is a circuit diagram of a tilting controller for the swash platein the third embodiment;

FIG. 21 is a front view showing, along with a tilting piston, a swashplate and a feedback mechanism of a tilting controller according to afourth embodiment of the invention;

FIG. 22 is a front view showing the swash plate of FIG. 21 which hasbeen tilted in a forward direction;

FIG. 23 is a front view showing the swash plate of FIG. 21 which hasbeen tilted in a reverse direction; and

FIG. 24 is a front view showing a swash plate and a feedback mechanismin a modification of the tilting controller.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, with reference to FIGS. 1 through 23, the tilting controllerof a variable displacement hydraulic pump according to the presentinvention is described more particularly by way of its preferredembodiments which are applied by way of example to a vehicle drivehydraulic circuit of a wheel type working vehicle like a wheel loader.

Shown in FIGS. 1 through 9 is a first embodiment of the presentinvention. In these figures, indicated at 1 is a swash plate typevariable displacement hydraulic pump as a variable displacementhydraulic pump. The hydraulic pump 1 is constituted by a casing 11,rotational shaft 13, cylinder block 14, valve plate 19 and swash plate21, which will be described hereinafter.

Further, the hydraulic pump 1 is rotationally driven from a prime mover2 like a Diesel engine which is coupled with a rotational shaft 13 as adrive source to supply pressure oil to a pair of main conduits 3A and3B. Through the main conduits 3A and 3B, the hydraulic pump 1 isconnected to a hydraulic motor 5, which will be described hereinafter,forming a so-called closed hydraulic circuit 4.

Indicated at 5 is a vehicle driving hydraulic motor as a hydraulicactuator. This hydraulic motor 5 is coupled, for example, with wheels 7of a wheel type working vehicle through a reducer 6. As pressure oil isfed to and from the hydraulic pump 1 through the main conduits 3A and3B, the wheels 7 are rotationally driven from the hydraulic motor 5 toput the working vehicle in travel.

Denoted at 11 is a casing which forms an outer shell of the hydraulicpump 1. As shown in FIGS. 2 and 3, the casing 11 is composed of atubular main casing 11A and front and rear casings 11B and 11C whichclose front and rear ends of the main casing 11A. Provided in the rearcasing 11C are a pair of passages 12A and 12B which are connected to themain conduits 3A and 3B shown in FIG. 1.

Further, as shown in FIG. 3, provided in an outer peripheral side of themain casing 11A is an slot 11D and a drain passage 11E, which areconnected into a valve housing 25 of a regulator 24 which will bedescribed hereinafter. A translation bar 33 is slidably fitted in theslot 11D in the main casing 11A through a guide member 34, as describedin greater detail hereinafter. The internal cavity of the casing 11forms a drain chamber which is connected to a tank 36 which will bedescribed hereinafter.

Indicated at 13 is a rotational shaft which is rotatably mounted in thecasing 11. Namely, the rotational shaft 13 is rotatably supported in thefront and rear casings 11B and 11C through bearings. At an end 13A whichis axially projected out of the front casing 11B, the rotational shaft13 is rotationally driven by the prime mover 2 which is shown in FIG. 1.

Designated at 14 is a cylinder block which is provided within the casing11 and rotatable integrally with the rotational shaft 13. A pluralnumber of axially extending cylinders 15 are provided within thecylinder block 14 at predetermined intervals in the circumferentialdirection.

Indicated at 16 are pistons which are slidably fitted in the cylinders15 in the cylinder blocks 14. When a swash plate 21, which will bedescribed hereinafter, is tilted in a forward or reverse direction, eachone of the pistons 16 is reciprocated within a cylinder 15 in step withrotation of the cylinder block 14 to repeat intake and discharge cycles.

At one end, the pistons 16 are projected out of the cylinders 15 of thecylinder block 14 in the axial direction of the rotational shaft 13, andshoes 17 are rockably attached to the projected ends of the pistons 16.

Indicated at 18 is an annular shoe holder which is adapted to hold therespective shoes 17 against the swash plate 21. More particularly, asshown in FIGS. 3 and 4, the shoe holder 18 is adapted to hold therespective shoes 17 against a sliding surface 21A of the swash plate 21,guaranteeing for each one of the shoes 17 to be put in sliding movementon the sliding surface 21A of the swash plate 21, drawing an annularlocus of movement.

Indicated at 19 is a valve plate which is provided in the casing 11,located between the rear casing 11C and the cylinder block 14. Thisvalve plate 19 is held in sliding contact with an end face of thecylinder block 14, supporting the cylinder block 14 for rotation withthe rotational shaft 13. As shown in FIG. 3, the valve plate 19 isprovided with a pair of inlet/outlet ports 19A and 19B of an eyebrowshape. These inlet/outlet ports 19A and 19B are communicated withpassages 12A and 12B in the rear casing 11C.

During rotation of the cylinder block 14, the inlet/outlet ports 19A and19B of the valve plate 19 are intermittently communicated with therespective cylinders 15, sucking operating oil into the respectivecylinders 15 through one of the passage 12A (or 12B) and deliveringpressure oil to the other one of the passage 12B (or 12A) afterpressurizing the operating oil by the pistons 16 in the respectivecylinders 15.

Indicated at 20 is a swash plate support member which is provided in thefront casing 11B and around the outer periphery of the rotational shaft13. This swash plate support member 20 is located on the rear side ofthe swash plate 21, and provided with a tilting support surface 20A fortiltably supporting the swash plate 21. As shown in FIG. 4, the tiltingsupport surface 20A is in the form of a concavely curved surface toguide sliding movements of the swash plate 21 in the directions ofarrows A and B and around a tilting center C.

Denoted at 21 is a swash plate which is tiltably mounted in the casing11 through the swash plate support member 20 to form a volume varyingportion. The swash plate 21 is provided with a sliding surface 21A atthe front side for the respective shoes 17 and a tilting guide surface21B of a convexly curved shape at the rear side which is fitted in thetilting support surface 20A of the swash plate support member 20.

In this instance, as shown in FIGS. 4 to 6, the tilting guide surface21B of the swash plate 21 is formed as an arcuate surface of radius Rfrom the tilting center C. The tilting center C is located on an axisline O-O which extends parallel with the rotational shaft 13. By the useof tilting actuators 22 and 23 which will be described hereinafter, theswash plate 21 is driven to tilt either in a forward direction (in thedirection of arrow A) or in a reverse direction (in the direction ofarrow B) from the neutral position or zero angle position shown in FIGS.4 and 7. At this time, the capacity (oil discharge rate) of thehydraulic pump 1 is controlled by the tilting angle θ of the swash plate21.

Indicated at 22 and 23 are a pair of tilting actuators for driving theswash plate 21 into a tilted position. As shown in FIGS. 2 to 5, thesetilting actuators 22 and 23 are constituted by cylinder bores 22A and23A which are formed in the main casing 11A on radially outer side ofthe cylinder block 14, tilting pistons 22C and 23C which are slidablyfitted in the cylinder bores 22A and 23A to define pressure chambers 22Band 23B between the cylinder bores 22A and 23A, respectively, and biassprings 22D and 23D located in the pressure chambers 22B and 23B,respectively, for constantly urging the tilting pistons 22C and 23Ctoward the swash plate 21.

In this instance, the tilting actuators 22 and 23 are so located in themain casing 11A as to radially confront each other across the cylinderblock 14, driving the swash plate 21 to tilt in the direction of arrow Aor B by the tilting piston 22C or 23C. Namely, as shown in FIGS. 3 and6, the pressure chambers 22B and 23B of the tilting actuators 22 and 23are connected to the control conduits 39B and 39A, which will bedescribed hereinafter, to receive or discharge tilting control pressuretherethrough.

When the tilting piston 23C is extended out of the cylinder bore 23A bythe tilting control pressure and the tilting piston 22C is contractedinto the cylinder bore 22A as shown in FIG. 5, the swash plate 21 isdriven by the tilting piston 23C to tilt in the direction of arrow A (ina forward direction). On the other hand, when the tilting piston 22C isextended out of the cylinder bore 22A and the tilting piston 23C iscontracted into the cylinder bore 23A, the swash plate 21 is driven bythe tilting piston 22C to tilt in the direction of arrow B (in a reversedirection).

Indicated at 24 is a regulator which functions as a volume control valvefor supplying tilting control pressure to and from the tilting actuators22 and 23. As shown in FIG. 3, the regulator 24 is constituted by avalve housing 25 which is provided on the casing 11 on the outer side ofthe main casing 11A, a control sleeve 26, spool 27, hydraulic pilotportion 28 and valve spring 29, which will be described hereinafter.Namely, as shown in FIG. 6, the regulator 24 is constituted by ahydraulic servo valve having a spool 27 within a control sleeve 26 forthe control of tilting.

In this instance, as shown in FIG. 3, tilting control pressureinlet/outlet ports 25A and 25B are provided in the valve housing 25 ofthe regulator 24. The input/output port 25A is connected to a deliveryside of a pilot pump 35 through a control conduit 37A which will bedescribed hereinafter. The other input/output port 25B is connected to acontrol conduit 37B which will also be described hereinafter. The valvehousing 25 of the regulator 24 is fixed liquid tight on the outer sideof the casing 11, and the control sleeve 26 and spool 27 are disposedparallel with the rotational shaft 13 (parallel with the axis line O-Oshown in FIG. 6).

Indicated at 26 is a tubular control sleeve which is slidably fitted inthe valve housing 25. At one end of axial direction of the controlsleeve 26, a translation bar 33, which will be described hereinafter, isintegrally connected to the outer periphery of the control sleeve bymeans of a plural number of set screws, so that the control sleeve 26 isput in sliding displacements within the valve housing 25 in axialdirections (in the directions of arrows D and E in FIG. 4) following themovements of the translation bar 33 (rectilinear movements along theaxial direction of the rotational shaft 13).

Indicated at 27 is a spool which is slidably fitted in the controlsleeve 26. As the control spool 27 is put in sliding movement on theinner peripheral side of the control sleeve 26 in the axial direction ofthe valve housing 25, the input/output port 25B is selectively broughtinto or out of communication with the input/output port 25A or a drainpassage 11E.

Denoted at 28 is a hydraulic pilot portion which is provided in thevalve housing 25 in association with one end of axial direction of thespool 27. This hydraulic pilot portion 28 is provided with a plunger 28Afor axially driving the spool 27 against a valve spring 29 which will bedescribed hereinafter, and supplied with a command pressure through acommand pressure conduit 42 which will also be described hereinafter.

Upon receiving a command pressure as a pilot pressure through thecommand pressure conduit 42, the plunger 28A of the hydraulic pilotportion 28 puts the spool 27 in an axial sliding movement in the valvehousing 25 according to the pilot pressure thereby switching theregulator 24 from a neutral position (Va) to a switched position (Vb) or(Vc) shown in FIG. 6.

Indicated at 29 is a valve spring which is interposed between the otherend of axial direction of the spool 27 and the valve housing 25. By theaction of this valve spring 29, the spool 27 is constantly urged towardthe hydraulic pilot portion 28, for example, to return the regulator 24to the neutral position (Va) shown in FIG. 6.

Indicated at 30 is a feedback mechanism adopted in the first embodimentof the invention. This feedback mechanism 30 is provided for feedbackcontrol of the regulator 24 by letting same follow tilting motions ofthe swash plate 21. In this instance, as shown in FIGS. 3 and 6, thefeedback mechanism 30 is constituted by a motion converting section 31and the translation bar 33, which are provided between a lateral side ofthe swash plate 21 and the control sleeve 26 of the regulator 24 asdescribed in greater detail hereinafter.

As the swash plate 21 is tilted from the neutral position in a forwardor reverse direction, the feedback mechanism 30 put the translation bar33 in a rectilinear movement along the axis line O-O of the rotationalshaft 13, which is a straight line passing through the tilting center Cof the swash plate 21.

Indicated at 31 is a motion converting section of the feedback mechanism30, functioning to convert a tilting motion of the swash plate 21 intoan axial displacement along the axis line O-O of the rotational shaft13. In this instance, the motion converting section 31 is constituted bya projection 32 as an active coupling member which is fixed on andprojected from an outer peripheral side of the swash plate 21, and aslider portion 33A as a passive coupling member which is provided on thetranslation bar 33 as described below.

The slider portion 33A of the translation bar 33 is slidably engagedwith the projection 32 on the side of the swash plate 21 to convert atilting motion of the swash plate 21 into an axial displacement as alongitudinal linear displacement along the axis line O-O. As shown inFIGS. 3 to 9, the projection 32 on the side of the swash plate 21 andthe slider portion 33A of the translation bar 33 are relatively slidablyengaged with each other.

Namely, the projection 32 and the slider portion 33A restrict movementsof the translation bar 33 relative to the swash plate 21 (relative tothe projection 32) in the direction of the axis line O-O of therotational shaft 13, while permitting relative movements of the swashplate 21 (the projection 32) and the translation bar 33 in a directionperpendicular to the axis line O-O of the rotational shaft 13.

In this instance, the projection 32 is formed in a round columnar shapeby the use of a bolt or pin which is fixedly planted on a lateral sideof the swash plate 21. When the swash plate 21 is located in the neutralposition of zero angle as shown in FIGS. 6 and 7, the projection 32 islocated in a perpendicularly intersecting position relative to the axisline O-O of the rotational shaft 13. Further, as shown in FIG. 7, theprojection 32 is located in a position at a radius Ra from the tiltingcenter C of the swash plate 21, the radius Ra being smaller than theradius R of the tilting guide surface 21B (Ra<R).

Indicated at 33 is the translation bar as a translation member whichconstitutes a displacement transmission member of the feedback mechanism30. As shown in FIG. 3, this translation bar 33 is slidably mounted inthe slot 11D in the main casing 11A through a guide member 34, whichwill be described hereinafter, for rectilinear movement along the axialdirection of the rotational shaft 13 (the axis line O-O shown in FIG.6). As shown in FIG. 3, the translation bar 33 is extended in the casing11 and through the radial direction of the rotational shaft 13 andlocated between outer peripheral side of the swash plate 21 and thecontrol sleeve 26.

In the particular embodiment shown, the translation bar 33 is providedwith a U-shaped slider portion 33A at one longitudinal end, which sliderportion 33A constitutes the motion converting section 31 in the feedbackmechanism together with the projection 32 on the side of the swash plate21. As shown in FIGS. 6 to 9, the slider portion 33A is extended in adirection perpendicular to the axis line O-O of the rotational shaft 13,and the projection 32 on the side of the swash plate 21 is slidablyengaged in the slider portion 33A.

When the swash plate 21 is in the neutral position, the slider portion33A of the translation bar 33 is located in an initial position of FIG.7 on a line F-F perpendicular to the axis line O-O of the rotationalshaft 13, together with the projection 32 of the swash plate 21. At thistime, the translation bar 33 is located in a fully receded positionalong the axis line O-O of the rotational shaft 13 in the direction ofarrow E in FIG. 6.

When the swash plate 21 is tilted from the neutral position in thedirection of arrow A (in a forward direction) until the tilt angle θreaches an angle α (θ=α) as shown in FIGS. 5 and 8, the projection 32 onthe swash plate 21 is turned to a position of angle α relative to theaxis line O-O. As a consequence, following the movement of theprojection 32, the slider portion 33A of the translation bar 33 istranslated to a position on line G-G in FIG. 8 (rectilinear movement),that is, displaced from the line F-F of the initial position by adistance a in the axial direction of the rotational shaft 13.

On the other hand, when the swash plate 21 is tilted from the neutralposition in the direction of arrow B (in a reverse direction) until thetilt angle θ reaches an angle β (θ=β) as shown in FIG. 9, the projection32 on the swash plate 21 is turned to a position of the angle β relativeto the axis line O-O. As a consequence, the slider portion 33A of thetranslation bar 33 is translated to a position on line H-H of FIG. 9following the movement of the projection 32, that is to say, displacedfrom the initial position on line F-F by a distance b in the axialdirection of the rotational shaft 13.

When the swash plate 21 is tilted in the forward or reverse directionthrough the same tilt angle θ (e.g., through the angle α or β, thesetilting angles α and β corresponding to the tilt angle θ of the swashplate 21 are equivalent angles in opposite directions (α=β) and bringabout the equivalent distances a and b corresponding to an axialdisplacement.

As shown in FIG. 3, the other longitudinal end of the translation bar 33is extended in the radial direction of the control sleeve 26, andprovided with a bifurcated anchor portion 33B at a distal end which isadapted to embrace the control sleeve 26 from radially outside. Theanchor portion 33B is securely fixed to the outer periphery of thecontrol sleeve 26 by a plural number of set screws or rivets.

Thus, the translation bar 33 is fixedly retained on the control sleeve26 at a predetermined angle relative to the latter (e.g., at an angle of90 degrees). As shown in FIGS. 4 to 6, following movements of thetranslation bar 33, the control sleeve 26 is displaced in the directionsof arrows D and E along the axis line O-O of the rotational shaft 13.

In this manner, as the swash plate 21 is tilted in a forward or reversedirection together with the projection 32, the tilting motion of theswash plate 21 is picked up as an axial displacement of the sliderportion 33A in the direction of axis line O-O of the rotational shaft 13(e.g., the distance a or b) by the motion converting section 31 havingthe projection 32 on the side of the swash plate 21 engaged with theslider portion 33A of the translation bar 33. The translation bar 33,which functions as a displacement transmission member, transmits anaxial displacement of the slider portion 33A to the control sleeve 26through the anchor portion 33B as a similar axial displacement.

Indicated at 34 is a guide member which is provided in such a manner asto cover the slot 11D in the casing 11. As shown in FIG. 3, the guidemember 34 is arranged to slidably support an longitudinally intermediateportion of the translation bar 33, preventing upward or downward rockingmovements (e.g., rocking movements in the circumferential direction ofthe cylinder block 14) or rattling movements of the translation bar 33to ensure smooth parallel movement (rectilinear movement) of the latterin the axial direction of the rotational shaft 13.

Thus, as the swash plate 21 is tilted in the direction of arrow A or Bin FIG. 2, the translation bar 33 of FIG. 3 is put in a parallelmovement in the axial direction of the rotational shaft 13, followingthe tilting motion of the swash plate 21. The parallel movement of thetranslation bar 33 is directly transmitted to the control sleeve 26 ofthe regulator 24 by the anchor portion 33B, for feedback control of theregulator 24.

Indicated at 35 is a pilot pump for generating a tilting controlpressure. This pilot pump 35 rotationally driven from the prime mover 2of FIG. 1 together with the hydraulic pump 1. While pumping in operatingoil, for example, from the tank 36 shown in FIG. 3, the pilot pump 35delivers a tilting control pressure to the control conduit 37A.

In this instance, by a low pressure relief valve 38, the tilting controlpressure which is delivered by the pilot pump 35 is maintained at asufficiently low level as compared with the output pressure of thehydraulic pump 1. The control conduit 37B is provided between theinlet/outlet port 25B of the regulator 24 and a forward/reversedirectional control valve 40 which will be described hereinafter.

Designated at 39A and 39B are other control conduits which supply atilting control pressure to and from pressure chambers 23B and 22B ofthe tilting actuators 23 and 22. As shown in FIGS. 3 and 6, the controlconduits 39A and 39B are switched over between the control conduits 37Aand 37B by the forward/reverse directional control valve 40 as describedbelow.

Indicated at 40 is a forward/reverse directional control valve as adirectional control valve which is connected between the controlconduits 37A and 37B and the control conduits 39A and 39B. As shown inFIGS. 3 and 6, this forward/reverse directional control valve 40 isprovided with left and right solenoids 40A and 40B. For example, bymanually operating a switch lever (not shown) which is provided in anoperator's room of the vehicle, this forward/reverse directional controlvalve 40 can be switched from a stop position (a) to a forward driveposition (b) or a reverse drive position (c).

When the forward/reverse directional control valve 40 switched from thestop position (a) to the forward drive position (b), tilting controlpressure from the pilot pump 35 is supplied to the pressure chamber 23Bof the tilting actuator 23 through the control conduits 37A and 39A,according to the extent of depression of a vehicle drive pedal 41A by anoperator's foot.

Further, at this time, tilting control pressure in the pressure chamber22B of the tilting actuator 22 is discharged to the side of the tank 36through the control conduits 39B and 37B and the regulator 24. As aresult, the swash plate 21 is driven to tilt in the direction of arrow Ain FIG. 6 by the tilting piston 23C of the tilting actuator 23.

On the other hand, when the forward/reverse directional control valve 40is switched to the reverse drive position (c) from the stop position(a), tilting control pressure from the pilot pump 35 is supplied to thepressure chamber 22B of the tilting actuator 22 through the controlconduits 37A and 39B, according to the extent of depression of a vehicledrive pedal 41A. Further, tilting control pressure in the pressurechamber 23B of the tilting actuator 23 is discharged to the side of thetank 36 through the control conduits 39A and 37B and the regulator 24.As a result, the swash plate 21 is driven to tilt in the direction ofarrow B in FIG. 6 by the tilting piston 22C of the tilting actuator 22.

In this manner, the forward/reverse directional control valve 40 isprovided between the regulator 24 and the tilting actuators 22 and 23 toswitch the vehicle drive position from the stop position (a) to theforward drive position (b) or reverse drive position (c). For changingthe vehicle drive position, the forward/reverse directional controlvalve 40 switches the direction of the tilting control pressure supplyto and from the tilting actuators 22 and 23, while driving the swashplate 21 in the neutral position to tilt in the forward or reversedirection, following the tilting control pressure.

Indicated at 41 is a vehicle operating valve which is provided as acommand means within an operating room of the wheel type vehicle. Asshown in FIG. 6, a vehicle drive pedal 41A corresponding to anaccelerator pedal is attached to the vehicle operating valve 41. Whenthe vehicle drive pedal 41A is pressed by an operator's foot, a pilotpressure is supplied as a command signal to the hydraulic pilot portion28 of the regulator 24 from the vehicle operating valve 41 via thecommand pressure conduit 42 for variably adjusting the traveling speedof the vehicle in the manner as described hereinafter.

According to the present embodiment, the vehicle drive hydraulic circuitfor a wheel type working vehicle with a swash plate type variabledisplacement hydraulic pump is arranged as described above, and put inoperation in the manner as follows.

In operation, when the forward/reverse directional control valve 40 ofFIG. 6 is in the stop position (a), both of the control conduits 39A and39B are connected to the control conduit 37A. At this time, the pressurechambers 22B and 23B of the tilting actuators 22 and 23 are maintainedat the same pressure level, and the swash plate 21 is retained in theneutral position of zero angle.

Therefore, even if the prime mover 2 is started to rotationally drivethe rotational shaft 13, putting the cylinder block 14 in rotation withthe rotational shaft, the pistons 16 are not reciprocated in therespective cylinders 15 of the cylinder block 14, and pressures in thepassages 12A and 12B in the hydraulic pump 1 remain at the same level.Accordingly, the hydraulic motor 5 of FIG. 1 remains at rest because nooil pressure is supplied thereto from the hydraulic pump 1 through themain conduits 3A and 3B.

In the next place, as soon as the forward/reverse directional controlvalve 40 in the stop position (a) is switched to the forward driveposition (b) by the operator, the tilting control pressure from thepilot pump 35 is supplied to the pressure chamber 23B of the tiltingactuator 23 through the control conduits 37A and 39A, according to thedegree of depression of the vehicle drive pedal 41A by an operator'sfoot.

Thus, at this time, as the vehicle drive pedal 41A is pressed by anoperator's foot, a pilot pressure is supplied toward the hydraulic pilotportion 28 of the regulator 24 from a command pressure conduit 42.Whereupon, the spool 27 in the valve housing 25 of the regulator 24makes a sliding displacement in the axial direction according to thepilot pressure to switch the regulator 24 to a switched position (Vb)from a neutral position (Va) shown in FIG. 6.

As a result, the control conduit 37B is connected to the tank 36 throughthe regulator 24 and the drain chamber within the casing 11, and tiltingcontrol pressure is discharged from the pressure chamber 22B of thetilting actuator 22 toward the tank 36 through the control conduit 39B,the forward/reverse directional control valve 40 in the forward driveposition (b), the control conduit 37B and the regulator 24.

At this time, the tilting control pressure from the pilot pump 35 issupplied to the pressure chamber 23B of the tilting actuator 23 throughthe control conduit 37A, the forward/reverse directional control valve40 in the forward drive position (b) and the control conduit 39A. By thetilting piston 23C of the tilting actuator 23, the swash plate 21 isdriven to tilt in the direction of arrow A in FIG. 6.

When the swash plate 21 is tilted in the direction of arrow A, byrotation of the cylinder block 14 with the rotational shaft 13, therespective pistons 16 are repeatedly reciprocated within the cylinders15 of the cylinder block 14 at a stroke volume (displacement volume)corresponding to the tilt angle θ. At this time, the hydraulic pump 1draws oil into the respective cylinders 15, for example, through thepassage 12A, while discharging oil from the passage 12B.

As a result, in the vehicle drive closed hydraulic circuit 4 of FIG. 1,pressure oil is circulated in the main conduits 3A and 3B in thedirection of arrow A1, rotationally driving the hydraulic motor 5 withpressure oil. Rotational output of the hydraulic motor 5 is transmittedto wheels 7 of the wheel type working vehicle through the reducer 6. Bydriving the wheels 7, the working vehicle is put in travel, for example,in a forward direction at a speed corresponding to the tilt angle θ.

On the other hand, when the forward/reverse directional control valve 40from the stop position (a) is switched to the reverse drive position(c), a tilting control pressure is supplied from the pilot pump 35 tothe pressure chamber 22B of the tilting actuator 22 through the controlconduits 37A and 39B, according to the extent of depression of thevehicle drive pedal 41A. Further, tilting control pressure is dischargedfrom the pressure chamber 23B of the tilting actuator 23 to the tank 36through the control conduits 39A and 37B and the regulator 24. As aresult, by the tilting piston 22C of the tilting actuator 22, the swashplate 21 is driven to tilt in the direction of arrow B in FIG. 6.

In this case, in the vehicle drive closed hydraulic circuit 4 shown inFIG. 1, pressure oil is circulated in the direction of arrow B1 forrotationally driving the hydraulic motor 5 in the same direction.Consequently, by transmitting the rotational output of the hydraulicmotor 5 to wheels 7 of the wheel type working vehicle through thereducer 6, the vehicle can be driven in the reverse direction at a speedcorresponding to the tilt angle θ.

When the vehicle is put in travel in forward or reverse direction, thevehicle speed is determined by the discharge rate (flow rate) ofpressure oil by the hydraulic pump 1, and the discharge rate isincreased or decreased depending upon the tilt angle θ of the swashplate 21. Unless the regulator 24, which is a volume control valve, isoperated under a feedback control according to the tilt angle θ of theswash plate 21, it is difficult to stably control the tilt angle θ ofthe swash plate (or the vehicle speed) solely by way of depressingoperations on the vehicle drive pedal 41A.

Therefore, according to the present embodiment, the feedback mechanism30 is provided between the control sleeve 26 of the regulator 24 and alateral side of the swash plate 21. As a result of feedback control bythis feedback mechanism 30, the regulator 24 is made to follow tiltingmotions of the swash plate 21 whenever the latter is driven to tilt froma neutral position of the zero angle to the forward or reverse directionby the tilting actuator 23 or 22.

The feedback mechanism 30 is constituted by the motion convertingsection 31 which translate a tilting motion of the swash plate 21 intoan axial displacement, and the translation bar 33 which is moved in theaxial direction of the rotational shaft 13, following tilting motions ofthe swash plate which are converted into axial displacements by themotion converting section 31. An axial displacement, converted by themotion converting section 31, transmitted to the control sleeve 26 ofthe regulator 24 through the anchor portion 33B at the distal end of thetranslation bar 33.

In this instance, the motion converting section 31 is constituted by thepin or round projection 32 which is fixed on a lateral side of the swashplate 21, and the U-shaped slider portion 33A which is provided at onelongitudinal end of the translation bar 33 in a direction perpendicularto the axis line O-O of the rotational shaft 13 and slidably coupledwith the projection 32. By the motion converting section 31, a tiltingmotion of the swash plate 21 is transmitted to the translation bar 33 asan axial displacement in the direction of the axis line O-O.

Therefore, when the swash plate 21 in the neutral position is tilted inthe direction of arrow A (in the forward direction) to a position wherethe tilt angle θ is an angle α (β=α) as shown in FIG. 8, the projection32 on the swash plate 21 is turned to a position of the angle α relativeto the axis line O-O, putting the slider portion 33A of the translationbar 33 in a parallel movement as far as a position of line G-G of FIG. 8following the movement of the projection 32.

When the projection 32, which is located at a radius Ra from the tiltingcenter C of the swash plate 21, is turned through an angle α, thetranslation bar 33 is displaced in the axial direction of the rotationalshaft 13 from an initial position on line F-F to a position on line G-G.This axial displacement can be obtained as a distance a by Equation (1)below.a=Ra×(1−cos α)   (1)

On the other hand, when the swash plate 21 in the neutral position istilted in the direction of arrow B (in the reverse direction) to aposition where the tilt angle θ is an angle β (θ=α) as shown in FIG. 9,the projection 32 on the swash plate 21 is turned to a position of theangle β relative to the axis line O-O, putting the slider portion 33A ofthe translation bar 33 in a parallel movement as far as a position online H-H of FIG. 9 following the movement of the projection 32.

When the translation bar 33 in the initial position on line F-F isdisplaced to the position on line H-H in the axial direction of therotational shaft 13, this axial displacement can be obtained as adistance b by Equation (2) below.b=Ra×(1−cos β)   (2)

In this manner, by the motion converting section 31, that is, by theprojection 32 on the swash plate 21 and the slider portion 33A of thetranslation bar 33, a tilting motion of the swash plate 21 is convertedinto an axial displacement (e.g., of distance a or b) in the directionof axis line O-O of the rotational shaft 13, and this axial displacementis transmitted from the translation bar 33 to the control sleeve 26through the anchor portion 33B.

Irrespective of the direction of a tilting motion of the swash plate 21,which is either in the direction of arrow A (forward direction) or inthe direction of arrow B (reverse direction), the tilting motion isconverted into an axial displacement of the same direction (in thedirection of arrow D in FIG. 6). Namely, no matter whether the swashplate 21 is tilted in the forward or reverse direction from the neutralposition, the control sleeve 26 of the regulator 24 is put in a slidingdisplacement in the same direction as the spool 27, permitting torealize smooth feedback control of the control sleeve 26.

Therefore, according to the present embodiment, even in a case where theswash plate type variable displacement hydraulic pump 1 is connected tothe hydraulic motor 5 by the use of the closed hydraulic circuit 4 shownin FIG. 1, the discharge rate (flow rate) of the pressure oil can becontrolled in both directions by tilting the swash plate 21 which servesas a volume varying portion in forward and reverse directions from theneutral position, permitting to control the vehicle speed according tothe tilt angle of the swash plate 21 smoothly in both forward andreverse drives of the vehicle.

Besides, the regulator 24 which serves as a volume control valve can beconstituted by a hydraulic servo valve of simple construction having thespool 27 within the control sleeve 26. Accordingly, it becomes possibleto simplify the construction of the tilting controller as a whole,including the tilting actuators 22 and 23, regulator 24 and feedbackmechanism 30, and to improve the efficiency of assembling work byreduction of assembling parts.

Further, the forward/reverse directional control valve 40 is providedbetween the regulator 24 and the tilting actuators 22 and 23. Thisarrangement makes it possible to simplify the construction of thetilting controller as a whole as compared with the prior art, includingthe regulator 24, and to improve productivity and cut production cost ofthe controller.

Furthermore, in addition to the closed hydraulic circuit 4 shown in FIG.1, the tilting controller of the hydraulic pump 1 can be applied tosupply pressure oil to a so-called open hydraulic circuit, supplyingpressure oil to and from a hydraulic actuator like a hydraulic motor.Thus, thanks to improved versatility, the tilting controller of thehydraulic pump 1 can be applied to both a closed hydraulic circuit andan open hydraulic circuit, and can enhance productivity.

Turning now to FIGS. 10 through 16, there is shown a second embodimentof the present invention. A feature of this embodiment resides in that afeedback mechanism is constituted by a tilting lever which is providedon a lateral side of a swash plate for tilting motion therewith, and atranslation member which is provided between the tilting lever and acontrol sleeve of a regulator. In the following description of thesecond embodiment, those component parts which are identical with thecounterparts in the foregoing first embodiment are simply designated bythe same reference numerals or characters to avoid repetitions of sameexplanations.

In the drawings, indicated at 51 is a swash plate type variabledisplacement hydraulic pump which is adopted by the present embodiment,and at 52 is a casing of the hydraulic pump 51. The casing 52 is builtsubstantially in the same way as the casing 11 in the foregoing firstembodiment. Namely, the casing 52 is composed of a main casing 52A, afront casing 52B, a rear casing 52C, a slot 52D and a drain passage 52E.

However, in this case, the casing 52 has the slot 52D and drain passage52E in different positions. A translation bar 63 is slidably fitted inthe slot 52D through a guide member 64, as described in greater detailhereinafter. The internal cavity of the casing 52 forms a drain chamberwhich is connected to the tank 36.

Indicated at 53 is a regulator which serves as a volume control valvefor supplying tilting control pressure to and from the tilting actuators22 and 23. This regulator 53 is built substantially in the same way asthe regulator 24 in the foregoing first embodiment. More specifically,as shown in FIG. 10, the regulator 53 is constructed of a valve housing54 which is provided on and attached to the outer side of the maincasing 52A of the casing 52, a control sleeve 55 which is provided inthe valve housing 54, a spool 56, a hydraulic pilot portion 57 and avalve spring 58.

As shown in FIG. 10, tilting control pressure inlet/outlet ports 54A and54B are provided in the valve housing 54 of the regulator 53. Theinlet/outlet port 54A is connected to the discharge side of the pilotpump 35 through the control conduit 37A, while the inlet/outlet port 54Bis connected to the control conduit 37B. The valve housing 54 of theregulator 53 fixed liquid-tight on the outer side of the casing 52, andthe control sleeve 55 and spool 56 are disposed to extend in parallelrelation with the rotational shaft 13 (in the direction of axis line O-Oin FIG. 13).

However, in this case, the regulator 53 has the hydraulic pilot portion57 and valve spring 58 located positions which are reversed in the axialdirection as compared with the counterparts in the first embodiment, andthe control sleeve 55 and spool 56 are put in a sliding displacement inan inverse direction. Plunger 57A of the hydraulic pilot portion 57receives a command pressure from a command pressure conduit 42 as apilot pressure. According to the received pilot pressure, the spool 56of the hydraulic pilot portion 57 is put in a sliding displacement in anaxial direction (a direction inverse to the sliding displacement in thefirst embodiment) within the valve housing 54 to switch the regulator 53from a neutral position (Va) to a switched position (Vb) or (Vc).

Indicated at 59 is a feedback mechanism according to the secondembodiment. This feedback mechanism 59 plays a role of feedback controlof the regulator 53, following tilting motions of the swash plate 21. Inthis instance, the feedback mechanism 59 is arranged substantially inthe same manner as the feedback mechanism 30 in the first embodiment,and provided with a motion converting section 60 and a translation bar63 which will be described hereinafter. However, in this case, thefeedback mechanism 59 differs from the counterpart in the firstembodiment in that it employs a tilting lever 61 which will be describedlater.

Denoted at 60 is a motion converting section of the feedback mechanism59. As shown in FIG. 10, the motion converting section 60 is constitutedby a tilting lever 61, projection 62 and slider portion 63A, which willbe described hereinafter. By the motion converting section 60, a tiltingmotion of the swash plate 21 is converted into an axial displacementalong the axis line O-O of the rotational shaft 13.

Indicated at 61 is a tilting lever which is provided at a lateral sideof the swash plate 21. As shown in FIG. 10, this tilting lever 61 isextended along a lateral side of the swash plate 21 and outer peripheryof the cylinder block 14 in parallel relation with the rotational shaft13. The tilting lever 61 is tilted together with the swash plate 21, andhas a function of magnifying an axial displacement of the motionconverting section 60 (e.g., distances a1 and b1 shown in FIGS. 15 and16) which will be described in greater detail hereinafter.

Indicated at 62 is a projection which is fixedly provided on a fore endportion of the tilting lever 61 as an active coupling member. Theprojection 62 is formed in a round columnar shape by the use of a boltor pin which is planted on a fore end portion of the tilting lever 61.When the swash plate 21 (the tilting lever 61) is in a zero angleneutral position as shown in FIGS. 13 and 14, the projection 62 islocated in a perpendicularly intersecting position relative to the axisline O-O of the rotational shaft 13. Further, as shown in FIG. 14, theprojection 62 is located at a distance La from the tilting center C ofthe swash plate 21, the distance La being larger than the radius R ofthe tilting guide surface 21B (La>R).

Indicated at 63 is a translation bar which functions as a translationmember constituting a displacement transmission member of the feedbackmechanism 59. This translation bar 63 is arranged substantially in thesame way as the translation bar 33 in the foregoing first embodiment.However, in this case, the translation bar 63 is provided between a foreend portion of the tilting lever 61 and the control sleeve 55 of theregulator 53.

Further, the translation bar 63 is slidably fitted in the slot 52D inthe main casing 52A through a guide member 64, which will be describedhereinafter, and put in a rectilinear movement along an axial directionof the rotational shaft 13 (along the axis line O-O shown in FIG. 13).As shown in FIG. 10, between a fore end portion of the tilting lever 61and the control sleeve 55, the translation bar 63 is extended throughthe casing 52 in the radial direction of the rotational shaft 13(cylinder block 14).

In this instance, one longitudinal end of the translation bar 63 formedinto a U-shaped slider portion 63A, which constitutes a motionconverting section 60 together with the projection 62 on the side of thetilting lever 61. As shown in FIG. 13, the slider portion 63A as apassive coupling member is extended in a direction perpendicular to theaxis line O-O of the rotational shaft 13, and slidably engaged with theprojection 62 on the part of the tilting lever 61.

When the swash plate 21 is in a neutral position, the slider portion 63Aof the translation bar 63 is located in an initial position of FIG. 14together with the projection 62 on the side of the tilting lever 61,namely, located on line F-F which perpendicularly intersects the axisline O-O of the rotational shaft 13. At this time, the translation bar63 is located in a most receded position in the direction of arrow D inFIG. 13 along the axis line O-O of the rotational shaft 13.

When the swash plate 21 is tilted in the direction of arrow A (forwarddirection) together with the tilting lever 61 from the neutral positionto a tilted position where the tilt angle θ is an angle α (θ=α) as shownin FIGS. 12 and 15, the projection 62 on the tilting lever 61 is turnedto the position of the angle a relative to the axis line O-O. As aresult, following the movement of the projection 62, the slider portion63A of the translation bar 63 is put in a parallel movement (arectilinear movement) to a position on line G-G in FIG. 15, which isdisplaced by a distance a1 in the axial direction of the rotationalshaft 13 from the initial position on line F-F.a1=La×(1−cos α)   (3)

On the other hand, when the swash plate 21 is tilted together with thetilting lever 61 in the direction of arrow B (reverse direction) fromthe neutral position to a position where the tilt angle θ is an angle β(θ=β), the projection 62 on the tilting lever 61 is turned to theposition of the angle β relative to the axis line O-O. As a result,following the movement of the projection 62, the slider portion 63A ofthe translation bar 63 is put in a parallel movement to a position online H-H in FIG. 16, which is displaced by a distance b1 from theinitial position on line F-F in the axial direction of the rotationalshaft 13.b1=La×(1−cos β)   (4)

In this manner, by the motion converting section 60, which isconstituted by the projection 62 on the side of the tilting lever 61 andthe slider portion 63A of the translation bar 63, a tilting motion ofthe swash plate 21 with the tilting lever 61 in the forward or reversedirection is converted into an axial displacement along the axis lineO-O of the rotational shaft 13 (e.g., a distance of a1 or b1 mentionedabove). This displacement is transmitted to the control sleeve 55 by thetranslation bar 63 as a similar axial displacement.

Further, the other longitudinal end of the translation bar 63 isextended radially direction toward the control sleeve 55 and providedwith a bifurcated anchor portion 63B at the distal end which is arrangedto hold the control sleeve 55 from radially outer sides. The anchorportion 63B is securely fixed to outer periphery of the control sleeve55 by means of a plural number of set screws or rivets. In so doing, thetranslation bar 63 is fixed and retained at a predetermined angle withthe control sleeve 55 (e.g., perpendicularly at 90 degrees). By thetranslation bar 63, the control sleeve 55 is displaced in the directionsof arrows D and E along the rotational shaft 13 (the axis line O-O).

Indicated at 64 is a guide member which is provided to lo cover the slot52D of the casing 52 shown in FIG. 10. This guide member 64 is arrangedto slidably support an longitudinally intermediate portion of thetranslation bar 63, preventing vibrations and saccadic movements of thetranslation bar 63 in upward and downward directions (e.g., in thecircumferential direction of the cylinder block 14), ensuring smoothparallel movements (rectilinear movements) of the translation bar 63 inthe axial direction of the rotational shaft 13.

Designated at 65 is a forward/reverse directional control valve which isprovided as a directional control valve between the control conduits 37Aand 37B and the control conduits 39A and 39B. As shown in FIGS. 10 and13, this forward/reverse directional control valve 65 is provided withsolenoids 65A and 65B at right and left axial ends, respectively.Further, the forward/reverse directional control valve 65 is manuallyswitched by an operator from a stop position (a) to a forward driveposition (b) or a reverse drive position (c), and operates substantiallyin the same manner as the forward/reverse directional control valve 40in the first embodiment.

Thus, also in the case of the second embodiment with arrangements asdescribed above, when the swash plate 21 is tilted in the direction ofarrow A or B in FIG. 13, the translation bar 63 is put in a parallelmovement in the axial direction of the rotational shaft 13 (in thedirection of arrow E), following a tilting motion of the swash plate 21and tilting lever 61. The parallel movement of the translation bar 63 isdirectly transmitted to the control sleeve 55 of the regulator 53through the anchor portion 63B for feedback control of the regulator 53,producing substantially the same operational effects as in the foregoingfirst embodiment.

However, in the case of the present embodiment, the tilting lever 61which is tiltable together with the swash plate 21 is employed.Consequently, as shown in FIG. 14, the projection 62 can be located at aposition which is at a greater distance La (La>R) from the tiltingcenter C of the swash plate 21, for the purpose of magnifying thedistance a1 and b1 in Equations 3 and 4 (distances of axialdisplacements of the translation bar 63) by way of the distance La.

Accordingly, when the spool 56 of the regulator 53 is put in a largesliding displacement in the axial direction by a pilot pressure (acommand signal) from the vehicle operating valve 41, the dimension offeedback control (the distance of axial displacement) of the controlsleeve 55 can be magnified to a larger scale to provide a stabilizedfeedback control of the control sleeve 55 of the regulator 53.

Now, turning to FIGS. 17 to 20, there is shown a third embodiment of thepresent invention. In short, this embodiment has features in that arocking link is employed for transmitting a tilting motion of a swashplate to a control sleeve of a regulator. In the following descriptionof the third embodiment, those component parts which are identical withthe counterparts in the foregoing first embodiment are simply designatedby the same reference numerals or characters to avoid repetitions ofsame explanations.

In the drawings, indicated at 71 is a swash plate type variabledisplacement hydraulic pump employed in the present embodiment, and at72 is a casing of the hydraulic pump 71. The casing 72 is builtsubstantially in the same manner as the casing 11 in the foregoing firstembodiment. Namely, the casing 72 is constituted by a tubular maincasing 72A, a front casing 72B, a rear casing 72C, a slot 72D and adrain passage 72E.

However, in this case of the casing 72, a rocking link 84, describedhereinafter, is pivotally supported in the slot 72D through the supportshaft 83 as shown in FIG. 17. The inner cavity of the casing 72 forms adrain chamber which is connected to the tank 36.

Indicated at 73 is a regulator which operates as a volume control valvefor supplying tilting control pressures to and from tilting actuators 22and 23. The regulator 73 is constructed substantially in the same manneras the regulator 24 in the foregoing first embodiment. As shown in FIG.17, the regulator 73 is constituted by a valve housing 74 which isprovided on the casing 72, more specifically, on the outer side of themain casing 72A, a control sleeve 75 which is provided within the valvehousing 74, a spool 76, a hydraulic pilot portion 77 and a valve spring78.

As shown in FIG. 17, the valve housing 74 of the regulator 73 isprovided with tilting control pressure inlet/outlet ports 74A and 74B,of which the inlet/outlet port 74A is connected to the discharge side ofthe pilot pump 35 through the control conduit 37A while the inlet/outletport 74B is connected to the control conduit 37B. Further, the valvehousing 74 of the regulator 73 is fixed liquid-tight on an outer side ofthe casing 72, with the control sleeve 75 and the spool 76 disposedparallel with the rotational shaft 13 (the axis line O-O shown in FIG.20).

However, in this case, the hydraulic pilot portion 77 and the valvespring 78 of the regulator 73 are located in inversed positions ascompared with the counterparts in the first embodiments. Accordingly,the control sleeve 75 and the spool 76 are each put in a slidingdisplacement in an inverse direction. Further, as a pilot pressure, theplunger 77A of the hydraulic pilot portion 77 receives a commandpressure from the command pressure conduit 42. Thus, according to thepilot pressure, the spool 76 is put in a sliding displacement in theaxial direction (in the opposite direction as compared with the firstembodiment) within the hydraulic pilot portion 77 to switch theregulator 73 of FIGS. 17 and 20 from a neutral position (Va) to aswitched position (Vb) or (Vc).

Indicated at 79 is a feedback mechanism according to the thirdembodiment. This feedback mechanism 79 plays the role of feedbackcontrol of the regulator 73, following tilting motions of the swashplate 21. In this instance, the feedback mechanism 79 is arrangedsubstantially in the same way as the feedback mechanism 30 in theforegoing first embodiment, and provided with a motion convertingsection 80 and a rocking link 84 which will be described hereinafter.However, in this case, the feedback mechanism 79 differs from thecounterpart in the first embodiment in that it employs the rocking link84 which is rockable about a support shaft 83 as described hereinafter.

Denoted at 80 is a motion converting section of the feedback mechanism79. By this motion converting section 80, a tilting motion of the swashplate 21 is converted into an axial displacement along the axis line O-Oof the rotational shaft 13. In this case, the motion converting section80 is constituted by a coupling pin 81 which is fixedly provided at alateral side of the swash plate 21 as an active coupling member, and aslider portion 84A which is provided on the rocking link 64 as passivecoupling member, as described hereinafter. A spherical projection 81A isprovided at the projected distal end of the coupling pin 81.

Indicated at 82 is a displacement transmission member of the feedbackmechanism 79, which is constituted by a support shaft 83 which isprovided in the slot 72D in the casing 72 and extended in a directionperpendicular to the axis of the rotational shaft 13, and a rocking link84 as described below.

Denoted at 84 is a rocking link which constitutes a displacementtransmission member 82 together with the support shaft 83. Similarly tothe translation bar 33 in the first embodiment, the rocking link 84 islocated between a lateral side of the swash plate 21 and the controlsleeve 75 of the regulator 73. The rocking link 84, however, differs inthat it is rockably supported by the support shaft 83 within the slot72D in the casing 72.

Namely, as shown in FIG. 17, the rocking link 84 is extended into thecasing 72 in the radial direction of the rotational shaft 13 (thecylinder block 14) in such a way as to be located between a lateral sideof the swash plate 21 and the control sleeve 75. The rocking link 84 isrockable about the support shaft 83 within the slot 72D of the casing 72in the directions of arrows J and K in FIG. 20.

In this instance, the rocking link 84 is provided with a slider portion84A of U-shape in cross section at one longitudinal end. This sliderportion 84A constitutes the motion converting section 80 together withthe projection 81A on the side of the swash plate 21. As shown in FIG.20, the slider portion 84A is extended in a direction perpendicular tothe axis line O-O of the rotational shaft 13, and constitutes a passivecoupling member to be held in sliding engagement with the projection81A.

Further, as shown in FIG. 20, the rocking link 84 is arranged to have alength L1 between the support shaft 83 and the projection 81A, and alength L2 between the support shaft 83 and a connecting pin 85, whichwill be described later. When the slider portion 84A is put in arectilinear movement (a parallel movement) in the direction of arrow Dor E as described hereinafter, the rocking link 84 on the side of theconnecting pin 85 is displaced inversely against the slider portion 84Ain the axial direction of the rotational shaft 13 at a rate of (L2/L1).

Namely, as the projection 81A of the coupling pin 81 is tilted togetherwith the swash plate 21 in the direction of arrow A or B from a zeroangle of neutral position, the slider portion 84A of the rocking link 84is put in a rectilinear movement in an axial direction of the rotationalshaft 13 (in the direction of axis line O-O in FIG. 20), for example,making an axial displacement in the direction of arrow D. At this time,the other longitudinal end of the rocking link 84 (the side of theconnecting pin 85) is rocked in the opposite direction to make adisplacement in the direction of arrow J in FIG. 20.

In this manner, by the motion converting section 80, which isconstituted by the projection 81A on the side of the swash plate 21 andthe slider portion 84A of the rocking link 84, a tilting motion of theswash plate 21 in the forward or reverse-direction is converted into anaxial displacement in the direction of axis line O-O of the rotationalshaft 13. At this time, the rocking link 84 is turned about the supportshaft 83 in the direction of arrow J or K, transmitting an inversedaxial displacement to the control sleeve 75 through a connecting pin 85,which will be described hereinafter.

Indicated at 85 is a connecting pin which is adopted to transmit arocking movement of the rocking link 84 to the control sleeve 75. Bythis connecting pin 85, the other longitudinal end of the rocking link84 is pivotally connected to the control sleeve 75. The control sleeve75 is displaced in the axial direction of the regulator 73 by theconnecting pin 85, following the rocking movement of the rocking link84.

At this time, the axial displacement of the control sleeve 75 ismagnified depending upon the ratio of the lengths of hands of therocking link 84 (L2/L1). The support shaft 83 which pivotally supports alongitudinally intermediate portion of the rocking link 84 also servesto suppress vibratory or saccadic movements of the rocking link 84 inupward and downward directions (e.g., in the circumferential directionof the cylinder block 14), ensuring smooth rocking displacements of therocking link 84.

Denoted at 86 is a forward/reverse directional control valve which isprovided as a directional control valve between the control conduits 37Aand 37B and the control conduits 39A and 39B. As shown in FIGS. 17 and20, this forward/reverse directional control valve 86 is provided withsolenoids 86A and 86B at right and left axial ends, respectively.Further, lo this forward/reverse directional control valve 86 ismanually switched by an operator from a stop position (a) to a forwarddrive position (b) or a reverse drive position (c), and operatessubstantially in the same manner as the forward/reverse directionalcontrol valve 40 in the foregoing first embodiment.

Thus, in the case of the present embodiment with the arrangements asdescribed above, when the swash plate 21 is tilted in the direction ofarrow A or B in FIG. 20, the slider portion 84A of the rocking link 84is also put in a parallel movement in the axial direction of therotational shaft 13 (in the direction of arrow D) following a tiltingmotion of the swash plate 21.

At this time, the rocking link 84 is turned about the support shaft 83in the direction of arrow J, and this rocking displacement istransmitted to the control sleeve 75 of the regulator 73 through theconnecting pin 85, producing substantially the same operational effectsas the foregoing first embodiment in terms of feedback control of theregulator 73.

However, in the case of the present embodiment, the rocking link 84 isrockably mounted on the support shaft 83 between the swash plate 21 andthe control sleeve 75. Therefore, as shown in FIG. 20, a tiltingdisplacement of the swash plate 21 is transmitted to the control sleeve75 on a magnified scale according to the ratio (L2/L1) of the lengths ofthe hands of the rocking link 84, that is, a ratio of the length L1 ofone hand extending from the support shaft 83 to the projection 81A tothe length L2 of the other hand extending from the support shaft 83 tothe connecting pin 85.

Thus, even when the spool 76 of the regulator 73 is put in a slidingdisplacement largely in the axial direction by a pilot pressure (acommand signal) from the vehicle operating valve 41, the distance offeedback control of the control sleeve 75 (the distance of axialdisplacement) is enlarged to provide a stabilized feedback control forthe control sleeve 75 of the regulator 73.

Now, turning to FIGS. 21 to 23, there is shown a fourth embodiment ofthe present invention. This embodiment has features in that atranslation bar is put in a rectilinear movement along a straight linewhich is inclined relative to the axis line of the rotational shaft,converting a tilting motion of the swash plate into a longitudinallinear displacement along the inclined straight line. In the followingdescription of the fourth embodiment, those component parts which areidentical with the counterparts in the foregoing first embodiment aresimply designated by the same reference numerals or characters to avoidrepetitions of same explanations.

In the drawings, indicated at 91 is a feedback mechanism adopted in thefourth embodiment. This feedback mechanism 91 is arranged substantiallyin the same way as the feedback mechanism 30 in the first embodiment,and provided with a motion converting section 92 and a translation bar94 as will be described hereinafter. However, in this case, the feedbackmechanism 91 differs from the first embodiment in that the translationbar 94, which will be described later, is put in a rectilinear movement(a parallel movement) along an inclined straight line O1-O1.

In this instance, as shown in FIGS. 21 to 23, the inclined straight lineO1-O1 is a straight line which passes through the tilting center C ofthe swash plate 21, and inclined through a predetermined angle γrelative to the axis line O-O of the rotational shaft 13. The angle γmay be either a positive angle or a negative angle. Namely, as shown inFIG. 21, the inclined straight line O1-O1 may be a straight line whichis inclined through an angle γ in the direction of arrow B relative tothe axis line O-O of the rotational shaft 13 or a straight line which isinclined through an angle γ in the direction of arrow A relative to theaxis line O-O of the rotational shaft 13.

Indicated at 92 is a motion converting section of the feedback mechanism91. Similarly to the motion converting section 31 in the foregoing firstembodiment, this motion converting section 92 is constituted by aprojection 93 and a slider portion 94A, which will be describedhereinafter. However, in the case of the motion converting section 92, atilting motion of the swash plate 21 is converted into a longitudinallinear displacement along the inclined straight line O1-O1.

Denoted at 93 is a projection which is fixedly provided at a lateralside of the swash plate 21 as an active coupling member. This projection93 is arranged substantially in the same way as the projection 32 in thefirst embodiment, and located at a distance Ra from the tilting center Cof the swash plate 21. However, as shown in FIG. 21, when the swashplate 21 is in a zero angle neutral position, the projection 93 islocated in a perpendicularly intersecting position relative to theinclined straight line O1-O1.

Indicated at 94 is a translation bar, i.e., a translating member in adisplacement transmission member of the feedback mechanism 91. Thistranslation bar 94 is arranged substantially in the same way as thetranslation bar 33 in the first embodiment. However, the translation bar94 differs from the translation bar 33 of the first embodiment in thatit is extended in a direction approximately perpendicularly intersectingthe inclined straight line O1-O1.

In this instance, the translation bar 94 is provided with a sliderportion 94A of U-shape in cross section at one longitudinal end toconstitute a motion converting section 92 in cooperation with theprojection 93 on the side of the swash plate 21. As shown in FIG. 21,the slider portion 94A as a pressure coupling member is extended in aperpendicularly intersecting direction relative to the inclined straightline O1-O1, and slidably engaged with the projection 93 on the side ofthe swash plate 21.

When the swash plate 21 is in the neutral position, the slider portion94A of the translation bar 94 is located in an initial position of FIG.21 together with the projection 93, on line F1-F1 which perpendicularlyintersects the inclined straight line O1-O1. At this time, thetranslation bar 94 is located in a most receded position in thedirection of arrow E1 in FIG. 21 along the inclined straight line O1-O1.

Further, when the swash plate 21 in the neutral position is tilted inthe direction of arrow A (in the forward direction) to a position wherethe tilt angle θ is an angle α (θ=α), the projection 93 on the swashplate 21 is turned to a position of angle α relative to the inclinedstraight line O1-O1 as shown in FIG. 22. Therefore, following themovement of the projection 93, the slider portion 94A of the translationbar 94 is put in a parallel movement (a rectilinear movement) as far asa position on line G1-G1 of FIG. 22, which is displaced by a distance a(see Equation 1) from the initial position on line F1-F1 in thelongitudinal direction of the inclined straight line O1-O1.

On the other hand, when the swash plate 21 in the neutral position istilted in the direction of arrow B (in the reverse direction) toposition where the tilt angle θ is an angle β (θ=β), the projection 93on the swash plate 21 is turned to a position of the angle β relative tothe inclined straight line O1-O1 as shown in FIG. 23. Therefore,following the movement of the projection 93, the slider portion 94A ofthe translation bar 94 is put in a parallel movement as far as theposition on line H1-H1 of FIG. 23, which is displaced by a distance bfrom the initial position on line F1-F1 in the longitudinal direction ofthe inclined straight line O1-O1.

In this manner, by the motion converting section 92 which is constitutedby the projection 93 on the side of the swash plate 21 and the sliderportion 94A of the translation bar 94, a tilting motion of the swashplate 21 in the forward or reverse direction is converted into alongitudinal linear displacement along the inclined straight line O1-O1(e.g., a displacement of a distance a or b). By the translation bar 94,this displacement is transmitted to the control sleeve 26 (see FIG. 6)as a similar longitudinal linear displacement.

Thus, in the case of the present embodiment with the arrangements asdescribed above, when the swash plate 21 is tilted in the direction ofarrow A or B of FIG. 21, the slider portion 94A of the translation bar94 is put in a parallel movement following the tilting movement of theswash plate 21, in the direction of arrow D1 or E1 along the inclinedstraight line O1-O1, producing substantially the same operationaleffects as in the foregoing first embodiment.

In the fourth embodiment described above, by way of example theprojection 93 of the motion converting section 92 is provided on alateral side of the swash plate 21. However, it is to be understood thatthe present invention is not limited to the particular arrangementsshown. For example, as in a modification shown in FIG. 24, a motionconverting section 92′ of a feedback mechanism 91′ may be located at aposition which is spaced from a lateral side of the swash plate 21.

In this instance, the motion converting section 92′ is constituted by atilting lever 61′ which is extended from a lateral side of the swashplate 21 along an inclined straight line O1-O1, a projection 93′ whichis provided on a fore end portion of the tilting lever 61′ as an activecoupling member, and a slider portion 94A′ which is provided on atranslation bar 94′ as a passive coupling member.

The tilting lever 61′ is substantially of the same construction as thetilting lever 61 in the foregoing second embodiment. However, thetilting lever 61′ in the modification is differs from the tilting lever61 in the second embodiment in that it is extended along an inclinedstraight line O1-O1.

Further, in the foregoing embodiments of the invention, as exemplifiedin FIG. 6, the vehicle operating valve 41 is employed as an externalcommand means, supplying the regulator 24 (53, 73) with a pilot pressureas a command signal commensurate with the extent of depression of thevehicle drive pedal 41A. However, needless to say, the present inventionis not limited to the particular arrangements shown. For example, it ispossible to incorporate an electromagnetic proportional solenoid intothe hydraulic pilot portion 28 (57, 77) of the regulator 24 (53, 77), incombination with an external command means which is adapted to produceas a command signal an electric signal commensurate with the extent ofdepression of the vehicle drive pedal 41A.

Further, in the foregoing embodiments, the tilting controller of theswash plate type variable displacement hydraulic pump 1 (51, 71) isapplied by way of example to a vehicle drive hydraulic circuit of awheel type working vehicle like a wheel loader. However, the presentinvention is applicable to various closed hydraulic circuits other thana vehicle drive hydraulic circuit, for example, to a hydraulic circuitfor a swing structure on a working vehicle.

Further, in the foregoing embodiments, the present invention has beendescribed by way of a tilting controller of a swash plate type variabledisplacement pump 1 (51, 71). However, it is to be understood thatapplication of the present invention is not limited to swash plate typevariable displacement pumps. For example, the present invention can alsobe applied to a bent axis type variable displacement pump in which avolume varying portion is constituted by a valve plate or the like.

Moreover, the present invention can be applied to various workingvehicles other than wheel loader. For example, the present invention canalso be applied to wheel type hydraulic excavators, wheel type hydrauliccranes, Bulldozers, working vehicles like lift trucks, or crawler typehydraulic excavator.

1. A tilting controller for a variable displacement hydraulic pump,including a variable displacement hydraulic pump having a volume varyingportion in association with a rotational shaft rotationally driven by adrive source, tilting actuators adapted to be applied with a tiltingcontrol pressure for driving said volume varying portion of saidhydraulic pump into a tilted position, a regulator in the form of aservo valve having a spool within a control sleeve for generating saidtilting control pressure to be fed to and from said tilting actuatorsaccording to a command signal from outside, and a feedback mechanismadapted to follow tilting motions of said volume varying portion to feedback said control sleeve of said regulator, characterized in that: saidvolume varying portion of said hydraulic pump is tiltable in bothforward and reverse directions from a zero angle neutral position drivenby said tilting actuators; said feedback mechanism is constituted by amotion converting section adapted to convert a tilting motion of saidvolume varying portion into a longitudinal linear displacement along astraight line passing through a tilting center (C) of said volumevarying portion, and a displacement transmission member located betweensaid motion converting section and said control sleeve of said regulatorto transmit said longitudinal linear displacement converted by saidmotion converting section to said control sleeve of said regulator, saiddisplacement transmission member being constituted by a translationmember (33, 63, 94, 94′) adapted to be put in a rectilinear movement inthe longitudinal direction of said straight line together with saidcontrol sleeve (26, 55) of said regulator (25, 53), following a tiltingmotion of said volume varying portion (21); said motion convertingsection being located in an initial position (F-F, F1-F1) at one end oflongitudinal direction along said straight line when said volume varyingportion is in a neutral position, and being displaced along and towardthe other end of longitudinal direction along said straight line fromsaid initial position (F-F, F1-F1) when said volume varying portion isdriven to tilt in forward or reverse direction.
 2. A tilting controllerfor a variable displacement hydraulic pump as defined in claim 1,wherein said straight line extends parallel with an axis line (O-O) ofsaid rotational shaft of said hydraulic pump and said motion convertingsection is adapted to convert a tilting motion of said volume varyingportion into an axial displacement in the direction of said axis line(O-O) of said rotational shaft.
 3. A tilting controller for a variabledisplacement hydraulic pump as defined in claim 1, wherein said straightline is an inclined straight line (O1-O1) drawn at a predetermined anglerelative to said rotational shaft of said hydraulic pump and said motionconverting section is adapted to convert a tilting motion of said volumevarying portion into a longitudinal linear displacement in the directionof said inclined straight line (O1-O1).
 4. A tilting controller for avariable displacement hydraulic pump as defined in claim 1, wherein adirectional control valve is provided between said tilting actuators andsaid regulator to switch direction of supply of said tilting controlpressure for driving to tilt said volume varying portion (21) in forwardor reverse direction from a neutral position.
 5. (canceled)
 6. A tiltingcontroller for a variable displacement hydraulic pump as defined inclaim 1, wherein said motion converting section of said feedbackmechanism is constituted by an active coupling member provided at alateral side of said volume varying portion at a position spaced from atilting center (C) of said volume varying portion, and a passivecoupling member provided at one longitudinal end of said displacementtransmission member extended in a perpendicularly intersecting directionrelative to said straight line and held in sliding engagement with saidactive coupling member.
 7. A tilting controller for a variabledisplacement hydraulic pump as defined in claim 6, wherein said activecoupling member of said motion converting section is constituted by aprojection provided on said volume varying portion to extend in a radialdirection relative to said straight line, and said passive couplingmember is constituted by a slider portion of U-shape in cross sectionslidably held in fitting engagement with said projection and extended ina perpendicularly intersecting direction relative to said straight line.8. A tilting controller for a variable displacement hydraulic pump asdefined in claim 1, wherein said motion converting section of saidfeedback mechanism is constituted by a tilting lever extended from saidvolume varying portion in the longitudinal direction of said straightline for tilting integrally with said volume varying portion, an activecoupling member provided on said tilting lever at a position spaced froma tilting center (C) of said volume varying portion, and a passivecoupling member provided at one longitudinal end of said displacementtransmission member to extend in a perpendicularly intersectingdirection relative to said straight line and held in sliding engagementwith said active coupling member.
 9. A tilting controller for a variabledisplacement hydraulic pump as defined in claim 8, wherein said activecoupling member of said motion converting section is constituted by aprojection provided on said tilting lever in a radial direction relativeto said straight line, and said passive coupling member is constitutedby a slider portion of U-shape in cross section slidably held in fittingengagement with said projection and extended in a perpendicularlyintersecting direction relative to said straight line.
 10. (canceled)11. (canceled)
 12. A tilting controller for a variable displacementhydraulic pump as defined in claim 11, wherein said active couplingmember of said motion converting section is constituted by a projectionprovided on said volume varying portion in a radial direction relativeto said straight line, and said passive coupling member is constitutedby a slider portion of U-shape in cross section slidably held in fittingengagement with said projection and extending in a perpendicularlyintersecting direction relative to said straight line.
 13. A tiltingcontroller for a variable displacement hydraulic pump as defined inclaim 1, wherein said control sleeve and spool of said regulator aredisposed to extend parallel with said straight line, and saiddisplacement transmission member is fixedly anchored to said controlsleeve.
 14. A tilting controller for a variable displacement hydraulicpump as defined in claim 1, wherein said hydraulic pump is comprised ofa tubular casing rotatably supporting said rotational shaft, a cylinderblock provided in said casing for rotation integrally with saidrotational shaft and containing a plural number of cylinders whichextend in axial direction at spaced positions in circumferentialdirection, a plural number of pistons fitted in said cylinders of saidcylinder block for reciprocating movements therein, and a swash platehaving a sliding surface for a shoe attached to an end of each pistonand tiltably mounted in said casing to constitute said volume varyingportion; said tilting actuators are located in said casing at a spacedposition from said rotational shaft in radially direction and havingtilting pistons for driving said swash plate in a neutral position totilt in a forward or reverse direction; said regulator is provided insaid casing at a spaced position from said tilting pistons with saidcontrol sleeve coupled with said swash plate through said feedbackmechanism; and an intermediate portion of said displacement transmissionmember of said feedback mechanism is mounted on said casing in such away as to permit displacements along the longitudinal direction of saidstraight line.